Diarrhea can cause a variety of fluid volume, acid-base, and electrolyte abnormalities. The alterations in serum chemistries that can occur, their etiologic mechanisms, and the issues related to diagnosis and treatment are reviewed in this topic.

FLUID AND ELECTROLYTE CONTENT OF NORMAL STOOL

The composition of normal stool must be known in order to understand the consequences of diarrhea:

●Normal stool has an alkaline pH.

●Sodium and potassium salts are the primary stool solutes. The sodium plus potassium concentration in stool usually ranges between 130 and 150 meq/L. Other cations, such as calcium and magnesium, are present at much lower concentrations.

●The main inorganic stool anions are bicarbonate (about 30 meq/L), chloride (about 10 to 20 meq/L), and a small amount of phosphate and sulfate.

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